1. Field of the Invention
This invention relates to a radar device, particularly to a target detection device and its detection method.
2. Brief Description of the Prior Art
Nowaday, radar device is widely applied for tracking and searching target. In order to enhance the accuracy of radar for tracking target in one respect and to reduce error so as to improve the accuracy of the radar device in another respect, the academic circle and the industries continuously propose the skill to improve the accuracy, such as an article entitled “A new tracker air-to-air missile targets” in the periodical IEEE Trans. Auto. Control, vol. 24, no. 6, December 1979 written by P. S. Maybeck, J. E. Negro, S. J. Cusmanao, and M. D. O. Jr., the radar device firstly obtains the target distance, the azimuth and the elevation angle, then the component values of the target are obtained. However, the convergence is unable to be finish in short duration so that this method can only be applied to detect the location of the target, and is unable to be used to estimate the location of target during the next time period. In another article entitled “Target tracking based on Kalman-type filters combination with recursive estimation model disturbances” in the periodical IEEE Radar Conf., pp. 115-120, May 2005 written by A. E. Nordsjo and S. B. Dynamics, the extended Kalman filter is used to reduce the error of relative acceleration obtained by the cooperation with the recursive prediction error method. However, the relative acceleration obtained is subject to big change, and thus is unstable.
In another article entitled “Estimation of chirp radar signals in compound-Gaussian clutter: A cyclostationary approach” in the periodical IEEE Trans. Signal Process., vol. 48, no. 4, pp. 1029-1039, April 2000 written by F. Gini, M. Montanari, and L. Verrazzani, the received signal is operated in correlation and the Doppler rate is obtained by Fourier series and maximum-likelihood estimation so as to determine the relative speed and the relative acceleration. However, 256 memory addresses are required for the acquisition of correlation, and 256 samples are needed for the operation of Fourier series and maximum-likelihood estimation so that the time required for the operation is huge. In another article entitled “Search radar detection and track with the Hough transform” in the periodical IEEE Trans. Aero. Electron. Syst., vol. 39, no. 1, pp. 1173-1177, July 1995 written by B. D. Carlson, E. D. Evans, and S. L. Wilson, the radar cooperates with matched filter and scans in the angular range from 0° to 180° by means of ρ=r cos θ+t sin θ and proceeds sampling per degree of angle. The point with densest concentration on the curve is regarded as ρ0 and θ0 which will then be substituted into the formula to obtain the relative distance r0. However, if there is an error, the calculation result will deviate greatly. Thus, the scanning should be proceeded in a very dense manner such that the number of operation is substantially increased. In still another article entitled “Robust range alignment via Hough transform in an ISAR image system” in the periodical IEEE Trans. Aero. Electron. Syst., vol. 31, no. 3, pp. 1173-1177, July 1995 written by T. Sauer and A. Schoitch, the radar cooperates with matched filter and scans in a given range of relative velocity v by r0=r(t)+v(t)t such that the point with densest concentration on the curve is regarded as the relative velocity v0 and the relative distance r0. Inasmuch as the range of relative velocity for scanning is known, the sampling number can be controlled at 30 so that accuracy can be raised. But, the r-v formed by using 30 samples is not precise enough.
In still another article entitled “Efficient approximation of Kalman filter for target tracking” in the periodical IEEE Trans. Aero. Electron. Syst., vol. 22, no. 1, pp. 8-14, January 1986 written by R. S. Baheti, convergence operation of 5 second duration has to be proceeded so as to reduce the error. However, the location of target is unable to be obtained instantaneously. In still another article entitled “Waveform design principle for automotive radar systems” in the periodical IEEE Radar, October 2001 written by H. Rohling and M. M. Meinecke, the combination of frequency-shift keying (FSK) method and linear frequency modulation (LFM) method is proposed. Each sensor can get two sets of signal at different frequencies such that each sample can provide one set of (r, v). However, the above system is unable to get relative acceleration. In still another article entitled “Velocity and acceleration estimation of Doppler weather radar/lidar signal in colored noised” in the periodical IEEE Acous. Speech Signal Process., vol. 3, pp. 2052-2055, 1995 written by W. Chen, G. Zhou, and G B. Giannakis, relative velocity and relative acceleration can be obtained by using the correlation among the 128 received samples and in cooperation with the multiple signal classification (MUSIC). However, the total operating time will be prolonged by the time required for sampling.
In still another article entitled as “Improved estimation of hyperbolic frequency modulated chirp signals” in the periodical IEEE Trans. Signal Process., vol. 47, no. 5, pp. 1384-1388, May 1999 written by O. Besson, G. B. Giannakis, N orders of sampling should be proceeded so as to obtain relative velocity and relative acceleration. Therefore, the time duration is quite long. In another article entitled “Robust two-stage Kalman filters for systems with unknown inputs” in the periodical IEEE Trans. Auto. Control, vol. 45, no. 12, pp. 2374-2378, December 2000 written by C. S. Hsieh, a linear system is provided that is incapable of performing operation treatment for non-linear condition. In another article entitled “Tracking systems for automotive radar networks” in the periodical IEEE Radar, pp. 339-343, October 2002 written by D. Oprisan and H. Rohling, three operation methods are disclosed. The first method has excessive number of operations so that the duration for operation is longer. The second and the third methods use extended Kalman filter to proceed operation which reduces the accuracy, though efficiency is increased.
In yet another article entitled as “A robust tracker with real time inputs estimation” in the periodical IEEE Signal Process., vol. 2, pp. 1529-1531, October 1998 written by F. Xinxi and X. Lizhen, the convergence time required to obtain the relative acceleration from the relative position and the relative velocity takes 20 seconds that might be too long to respond to a maneuvering target. In still another article entitled “An alternate derivation and extension of Friendland's two-stage Kalman estimator” in the periodical IEEE Trans. Auto. Control, vol. 26, no. 3, pp. 746-750, June 1981 written by M. B. Ignagni, the relative velocity and the relative acceleration can be obtained from the observed relative position. However, the components on X and Y axes cannot be obtained. In yet another article entitled “An automotive radar network based on 77 GHz FMCW sensors” in the periodical IEEE Radar Conf., pp. 871-876, May 2005 written by F. Folster, H. Rohling and U. Lubbert, operation is proceeded by using of extended Kalman filter directly to obtain the components of position and velocity. However, the relative velocity and the relative position are not obtained at first hand, so that the accuracy in the relative acceleration is reduced.
In still another article entitled as “Adaptive interacting multiple model tracking of maneuvering targets” in the periodical IEE Proc.-Radar Sonar Naving., vol. 42, no. 1, pp. 11-17, February 1985 written by J. R. Layne and C. Piyasena, the components on X and Y axes should be obtained firstly so that the relative acceleration can be obtained according to five two-stage Kalman filters. However, complexity in the operation is increased. In yet another article entitled “General two-stage extended Kalman filters” in the periodical IEEE Trans. Auto. Control, vol. 48, no. 2, pp. 289-293, February 2003 written by C. S. Hsieh, the extended two-stage Kalman filter is directly used to compute components of the position, the velocity and the acceleration on X and Y axes from the measured relative distance and the relative velocity. However, the accuracy of the acceleration is reduced. In still another article entitled “Maneuver target tracking with acceleration estimation using target past positions” in the periodical IEEE Radar, pp. 718-722, October 2001 written by M. Hashiro, T. Kwase and I. Sasase, the samples in the preceding three samplings are used to estimate the relative acceleration during the next time period, and then the components of the position and the velocity on X and Y axes can be computed using the weight coefficient. However, the acceleration with direction change cannot be estimated.
In yet another article entitled “An explicit high-resolution DOA estimation formula for two wave source” in the periodical IEEE Acous. Speech Signal Process., vol. 4, pp. 893-896, 2006 written by K. Ichige, N. Takabe, and H. Arai, two hundred samples are used to calculate the correlation, so the marching direction is obtained from the matrix of correlation and the distance from the target is operated. However, sampling of N times should be proceeded firstly, then the operation can be proceeded later. In still another article entitled “Simultaneous registration and fusion of multiple dissimilar sensors for cooperative driving” in the periodical IEEE Trans. Intell. Transp. Syst., vol. 5, no. 2, pp. 84-98, June 2004 written by W. Liand and H. Leung, an unscented Kalman filter is used to obtain the components of position, velocity and acceleration as well as the angle in horizontal direction and the angle in vertical direction. However, the convergence time is required to obtain the relative acceleration from the relative position and the relative velocity is 15 seconds which might be too long to respond to a maneuvering target. In yet another article entitled “General two-stage Kalman filters” in the periodical IEEE Trans. Auto. Control, vol. 45, no. 4, pp. 819-824, April 2000 written by C. S. Hsieh and F. C. Chen, the sampling time is 10 seconds and the simulation time is 500 seconds. Only the position can be detected with such short-period detection, and the position estimation during the next time period is unable to be proceeded.
In FIG. 1, a block diagram of a conventional target detection device is shown. As shown in the figure, the conventional target detection device 10 comprises a transmitting unit 12, a plurality of measuring units 14 and an extended Kalman filter 16, in which the extended Kalman filter 16 is connected to the plural measuring units 14. The transmitting unit 12 transmits detecting pulse 122 to a target 20 which will then reflect the detecting pulse 122 to generate a reflected pulse 202. The reflected pulse 202 is received respectively by the plural measuring units 14 which generate measured values of relative distance and relative velocity according to the reflected pulse 202. The extended Kalman filter 16 generates directly the components of the distance, the velocity and the acceleration in X and Y axes according to the measured values generated by the plural measuring units 14. As shown in FIGS. 2A to 2F, the detection errors of the conventional target detection device 10 are shown. The X coordinate axes of FIGS. 2A to 2F are all t/Tp which is a time parameter. While the Y axes of FIGS. 2A to 2F are error values. The values {circumflex over (x)}(t), ŷ(t), {circumflex over (v)}x(t), {circumflex over (v)}y(t), âx(t) and ây(t) are the detection values obtained by using the conventional target detection device 10 to detect the target. The values x(t), y(t), vx(t), vy(t), ax(t) and ay(t) are the real values. It is apparent from FIGS. 2A to 2F that between 1000 Tp≦t≦3000 Tp, the error value of the X component of the distance detected by the conventional target detection device 10 is about 380 cm, while the error value of the Y component of the distance is about 80 cm; the error value of the X component of the velocity is about 4.8 m/sec, while the error value of the Y component of the velocity is about 1.9 m/sec; the error value of the X component of the acceleration is about −90 m/sec2, while the error value of the Y component of the acceleration is about 35 m/sec2. Apparently from the figures, the conventional target detection device 10 is unable to reduce the error values effectively. Thus, the accuracy of the conventional target detection device 10 is low.
Therefore, it has always been an expectation from the user as how to provide a novel detection device aiming at the solution of above problems, which not only can improve inherent defects of prior art, but also can finish operation promptly and raise the operation accuracy. In view of the above fact, inventor of this invention thus proposes a new target detection device and its detection method to cope with the above problems.